US4661791A - Reed switch with high insulation - Google Patents

Reed switch with high insulation Download PDF

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Publication number
US4661791A
US4661791A US06/732,464 US73246485A US4661791A US 4661791 A US4661791 A US 4661791A US 73246485 A US73246485 A US 73246485A US 4661791 A US4661791 A US 4661791A
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United States
Prior art keywords
reed switch
high insulation
insulation
switches
reed
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Expired - Lifetime
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US06/732,464
Inventor
Tomio Wakasugi
Akinori Maeda
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Agilent Technologies Inc
Original Assignee
Hewlett Packard Co
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Publication date
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Assigned to HEWLETT-PACKARD COMPANY, A CORP. CA. reassignment HEWLETT-PACKARD COMPANY, A CORP. CA. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: MAEDA, AKINORI, WAKASUGI, TOMIO
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Publication of US4661791A publication Critical patent/US4661791A/en
Assigned to HEWLETT-PACKARD COMPANY, A DELAWARE CORPORATION reassignment HEWLETT-PACKARD COMPANY, A DELAWARE CORPORATION MERGER (SEE DOCUMENT FOR DETAILS). Assignors: HEWLETT-PACKARD COMPANY, A CALIFORNIA CORPORATION
Assigned to AGILENT TECHNOLOGIES INC. reassignment AGILENT TECHNOLOGIES INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HEWLETT-PACKARD COMPANY, A DELAWARE CORPORATION
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/64—Protective enclosures, baffle plates, or screens for contacts
    • H01H1/66—Contacts sealed in an evacuated or gas-filled envelope, e.g. magnetic dry-reed contacts

Definitions

  • the present invention relates to a reed switch with high insulation for a very low current measurement system.
  • Takuo Banno has indicated in Japanese Utility Model Laid-Open No. 57-131743, which has been assigned to Yokogawa-Hewlett-Packard Co., Ltd., that there is an unfavorable effect on signals caused by insulation resistance of switches, especially when measuring very low amplitude signals. Therefore, in the above-named Japanese Utility Model, Banno has proposed a particular combination of multiple switches to avoid such effects.
  • the resistivity of its insulation may generally be only approximately 10 9 ⁇ in a non-hostile environment, because of the leakage current on its glass-made surface. For very low current measurement, such order of insulation resistance is too low for measurement as is also suggested by Banno in the aforementioned Japanese Utility Model.
  • Improved insulation resistance of a reed switch could be achieved by washing or silicon coating. However, such treatment may not be effective for very low current measurement under high temperature and humid conditions in which its insulation resistance could still be less than 10 12 ⁇ .
  • a primary object of the present invention is to provide a reed switch with high insulation which can be used as matrix switches and scanners for very low current measurement even under high temperature and humid conditions.
  • a reed switch with high insulation which can be effectively used for very low current measurement (e.g., a switch matrix), is provided by coating over its glass-made surface with fluoroplastics materials.
  • the reed switch of this invention has obtained excellent characteristics as regards insulated resistance, offset current, dielectric absorption, etc., under high temperature and humid conditions and also furnishes an increased number of channels in measurement, especially for very low currents.
  • FIG. 1 is a cross-sectional view of a reed switch with high insulation in the embodiment of the present invention.
  • the present invention provides an improved reed switch coated with fluorocarbon polymer over the surface thereof.
  • FIG. 1 is a cross-sectional view of a reed switch according to the preferred embodiment of this invention.
  • the surface of the glass tube 15 of a reed switch that contains wire leads 11 and 13 is sufficiently washed, and then fully coated with fluorocarbon polymer 17 over the outer surface as shown in FIG. 1.
  • fluorocarbon polymer coating material can be chosen appropriately from those commercially available in the market. Coating method can be done by various methods as spraying, dipping, etc.
  • the average resistivity of the insulator was measured at 2 ⁇ 10 16 ⁇ (9 ⁇ 10 15 ⁇ was a minimum) at a temperature of 23° C. and humidity at 50%.
  • the average resistivity of the insulation was found to be 5 ⁇ 10 15 ⁇ (1.8 ⁇ 10 15 ⁇ was a minimum) which showed very small deterioration of resistivity of the insulation. Moisture resistivity for offset current and dielectric absorption were also improved.
  • Number of Switches ((Number of Input Channels) ⁇ 3+1).
  • the number of required switches with high insulation is reduced to the number of input channels.
  • the number of channels available is limited to as few as 10.
  • a scanner can be built with the channel number more than 1000.

Abstract

A reed switch with high insulation for a very low current measurement system is provided. The reed switch is embodied by coating over its glass-made surface with fluoroplastics materials in order to reduce the leakage current on the surface.

Description

BACKGROUND
The present invention relates to a reed switch with high insulation for a very low current measurement system.
Previously, Takuo Banno has indicated in Japanese Utility Model Laid-Open No. 57-131743, which has been assigned to Yokogawa-Hewlett-Packard Co., Ltd., that there is an unfavorable effect on signals caused by insulation resistance of switches, especially when measuring very low amplitude signals. Therefore, in the above-named Japanese Utility Model, Banno has proposed a particular combination of multiple switches to avoid such effects. When a reed switch is used as said switch, the resistivity of its insulation may generally be only approximately 109 Ω in a non-hostile environment, because of the leakage current on its glass-made surface. For very low current measurement, such order of insulation resistance is too low for measurement as is also suggested by Banno in the aforementioned Japanese Utility Model.
Improved insulation resistance of a reed switch could be achieved by washing or silicon coating. However, such treatment may not be effective for very low current measurement under high temperature and humid conditions in which its insulation resistance could still be less than 1012 Ω.
A primary object of the present invention is to provide a reed switch with high insulation which can be used as matrix switches and scanners for very low current measurement even under high temperature and humid conditions.
SUMMARY OF THE INVENTION
According to the present invention, a reed switch with high insulation, which can be effectively used for very low current measurement (e.g., a switch matrix), is provided by coating over its glass-made surface with fluoroplastics materials.
The reed switch of this invention has obtained excellent characteristics as regards insulated resistance, offset current, dielectric absorption, etc., under high temperature and humid conditions and also furnishes an increased number of channels in measurement, especially for very low currents.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a reed switch with high insulation in the embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Our intensive experiments have revealed that it is the surface condition of the glass-made wall of a reed switch that dominates the resistivity of its insulation. The present invention provides an improved reed switch coated with fluorocarbon polymer over the surface thereof.
FIG. 1 is a cross-sectional view of a reed switch according to the preferred embodiment of this invention. The surface of the glass tube 15 of a reed switch that contains wire leads 11 and 13 is sufficiently washed, and then fully coated with fluorocarbon polymer 17 over the outer surface as shown in FIG. 1. Such fluorocarbon polymer coating material can be chosen appropriately from those commercially available in the market. Coating method can be done by various methods as spraying, dipping, etc. As a result of the evaluation of the insulator resistivity of many reed switches embodied by this invention, the average resistivity of the insulator was measured at 2×1016 Ω (9×1015 Ω was a minimum) at a temperature of 23° C. and humidity at 50%. At a temperature of 40° C. and humidity at 70%, the average resistivity of the insulation was found to be 5×1015 Ω (1.8×1015 Ω was a minimum) which showed very small deterioration of resistivity of the insulation. Moisture resistivity for offset current and dielectric absorption were also improved.
These improvements can also result in more efficient circuit design. For instance, in Japanese Utility Model Laid Open No. 57-131743, mentioned above, the number of required prior art reed switches with high insulation per output channels may be determined by the formula: Number of Switches=((Number of Input Channels)×3+1). However, when the reed switches of this invention are used, the number of required switches with high insulation is reduced to the number of input channels.
Accordingly, when a measurement with a resolution of 1fA (10-15 A) is performed using the switches in the prior art, the number of channels available is limited to as few as 10. However, using the reed switches with the high insulation of this invention, a scanner can be built with the channel number more than 1000.

Claims (2)

We claim:
1. A reed switch with high insulation comprising:
a pair of conducting leads for selectively making contact; and
an enclosure for enclosing said pair of leads, an outer surface of said enclosure being coated with a fluoroplastic, said fluoroplastic providing high electrical insulation between said pair of conducting leads.
2. The reed switch with high insulation as set forth in claim 1, wherein said enclosure is made of glass.
US06/732,464 1984-05-29 1985-05-08 Reed switch with high insulation Expired - Lifetime US4661791A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP1984079239U JPH062176Y2 (en) 1984-05-29 1984-05-29 High isolation lead switch
JP59-79239[U] 1984-05-29

Publications (1)

Publication Number Publication Date
US4661791A true US4661791A (en) 1987-04-28

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Family Applications (1)

Application Number Title Priority Date Filing Date
US06/732,464 Expired - Lifetime US4661791A (en) 1984-05-29 1985-05-08 Reed switch with high insulation

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US (1) US4661791A (en)
JP (1) JPH062176Y2 (en)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5286932A (en) * 1991-07-26 1994-02-15 Gec Alsthom Sa Vacuum bulb provided with electrical insulation
WO1994027309A1 (en) * 1993-05-11 1994-11-24 General Datacomm, Inc. Transformed current sensing relay for use in switched network modems and circuit incorporating same
US5742216A (en) * 1995-04-05 1998-04-21 Hewlett-Packard Company Contact making and breaking device and system for measuring low current
US5880540A (en) * 1995-09-01 1999-03-09 Hewlett-Packard Company Switching apparatus with current limiting circuit
US20100001033A1 (en) * 2008-07-03 2010-01-07 Hsien-Cheng Chen Dry fire warning device for hammer tacker
US11309140B2 (en) * 2019-01-04 2022-04-19 Littelfuse, Inc. Contact switch coating

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US684094A (en) * 1901-02-14 1901-10-08 George Westinghouse Heater cut-out for electric lamps.

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4435724A (en) * 1981-09-10 1984-03-06 Wells Electronics, Inc. Single piece carrier for integrated circuit devices

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US684094A (en) * 1901-02-14 1901-10-08 George Westinghouse Heater cut-out for electric lamps.

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5286932A (en) * 1991-07-26 1994-02-15 Gec Alsthom Sa Vacuum bulb provided with electrical insulation
WO1994027309A1 (en) * 1993-05-11 1994-11-24 General Datacomm, Inc. Transformed current sensing relay for use in switched network modems and circuit incorporating same
US5426698A (en) * 1993-05-11 1995-06-20 General Datacomm, Inc. Transformed current sensing relay for use in switched network modems and circuit incorporating same
US5742216A (en) * 1995-04-05 1998-04-21 Hewlett-Packard Company Contact making and breaking device and system for measuring low current
US5880540A (en) * 1995-09-01 1999-03-09 Hewlett-Packard Company Switching apparatus with current limiting circuit
US20100001033A1 (en) * 2008-07-03 2010-01-07 Hsien-Cheng Chen Dry fire warning device for hammer tacker
US11309140B2 (en) * 2019-01-04 2022-04-19 Littelfuse, Inc. Contact switch coating
US20220122784A1 (en) * 2019-01-04 2022-04-21 Littelfuse, Inc. Contact switch coating

Also Published As

Publication number Publication date
JPS60192323U (en) 1985-12-20
JPH062176Y2 (en) 1994-01-19

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